McCartney, one of two surviving members of arguably the most successful pop band in history, told BBC Radio that “Carnival of Light” was The Beatles at their most free, “going off piste.”

“I said it would be great to put this on because it would show we were working with really avant-garde stuff,” McCartney told Radio 4’s Front Row culture show in an interview to be broadcast on Thursday.

He confirmed that he had a master tape of the track, which many Beatles fans assumed until now was a piece of musical myth, and added: “The time has come for it to get its moment.”

The 14-minute track was made for an electronic music festival, the only occasion the music was played in public.

“I said all I want you to do is just wander around all the stuff, bang it, shout, play it, it doesn’t need to make any sense,” McCartney told the program.

“Hit a drum then wander on to the piano, hit a few notes, just wander around. So that’s what we did and then put a bit of an echo on it. It’s very free.”

In order for Carnival of Light to be released, McCartney would have to get the agreement of Ringo Starr and the estates of John Lennon and George Harrison. According to the BBC, McCartney had wanted to include the track on The Beatles’ Anthology compilations in the mid-1990s, but the rest of the band vetoed the idea.